CaSAP8-CaDSK2a Negative Feedback Loop Modulates Pepper Thermotolerance by Integrating Transcriptional Repression and Protein Degradation.

Heat stress severely threatens crop productivity by disrupting cellular proteostasis and stress signalling. Selective protein degradation mediated by ubiquitin receptors and transcriptional regulation both play critical roles in plant stress responses, yet how these two layers are mechanistically integrated to regulate thermotolerance remains unclear. Here, we report that the ubiquitin receptor CaDSK2a and the transcription factor CaSAP8 form a negative feedback loop to modulate thermotolerance in pepper (Capsicum annuum L.). Yeast two-hybrid screening and multiple in planta assays demonstrate that CaDSK2a physically interacts with CaSAP8. Functional analyses reveal that CaSAP8 acts as a positive regulator of thermotolerance, as its silencing compromises heat tolerance, whereas its overexpression enhances thermotolerance in both pepper and tomato. Further analyses show that CaDSK2a promotes the selective autophagic degradation of CaSAP8, thereby attenuating thermotolerance. Conversely, CaSAP8 directly binds to the CaDSK2a promoter and represses its transcription. Genetic analyses further show that CaDSK2a is epistatic to CaSAP8 in regulating thermotolerance. Together, these findings support a model in which CaSAP8 and CaDSK2a form a negative feedback loop that dynamically modulates thermotolerance in pepper. This study reveals a regulatory module linking transcriptional regulation with protein degradation and provides new insights into the mechanisms that fine-tune thermotolerance in plants.